Disturbances in the delivery of power to end user equipment are presently quite common. These disturbances may be brownout disturbances in which low power levels are delivered, or complete blackout situations in which no power is delivered. These disturbances occur for a variety of reasons but are frequently related to high demand situations (i.e., hot summer days when air conditioners and other end user equipment are run at peak levels) or delivery system equipment maintenance or failure.
Such disturbances that result in brownout or blackout situations can cause damage to end user equipment when voltage levels delivered to the equipment fall below required levels. This damage can cost end users a significant amount of money to either repair or replace the damaged equipment. An example of such disturbance is line under voltage (LUV), such that the voltage of the supplied electricity is too low for some equipment, such as electric motors. If the voltage supplied to a motor is too low, the motor may fail to start or continue to rotate under a condition called locked rotor. With a locked rotor, all electric energy input to such motor is converted to heat and no energy is converted to motion. Under such locked rotor conditions an electric motor can heat up to a temperature that will cause thermal damage to some component or element of the motor, causing permanent damage. In addition, if there is no motion energy from the motor, the motor is not supplying the necessary energy needed to avoid a secondary failure, for example if a cooling fan is not turning, the component to be cooled may generate excess heat that can cause damage to some component or element of a system. Additionally, the motor with a locked rotor has a lower power factor than a motor that is delivering mechanical energy. Reduced power factors require utilities to generate additional electrical power to provide the energy being consumed by their customers, or for the utility to add additional capacitance to improve the power factor. Additionally, brownout or blackout situations cause utilities to lose revenue for energy that is not being consumed by their customers, and may damage their own delivery system equipment, requiring repair or replacement. Further, an isolated disturbance can affect a large number of end users if an entire subsystem load must be shed in response to the disturbance.
Presently, systems exist in which utilities monitor and control end user equipment remotely to control load levels. These systems, however, are controlled by the utility and are primarily only used in peak demand situations. These systems typically do not operate to protect end user equipment in non-peak demand situations. Further, present systems may not provide a sufficiently rapid response to decreasing power delivery levels to protect end user equipment from damage; it may take a utility control center operator several minutes or more to respond to a system disturbance.
There is a need in the industry for a system that protects end user equipment and electric distribution equipment from electric distribution power delivery disturbances, such system being automatic in its response for disconnecting and reconnecting the equipment to the electric distribution network, and that eliminates or substantially reduces the need for utilities to directly monitor the equipment and load levels for line under voltage conditions.